1. Field
The present invention relates to an electric brake device of a type equipped with a parking lock mechanism and, more particularly, to the technology of preventing the electric brake device from being frozen with no need of releasing a braking force.
2. Description of the Related Art
In general, a vehicle is inhibited from moving with the utilization of a parking brake that is mechanically independent from a so-called foot operated brake (also called “service brake”). However, particularly during the winter season and at cold districts, it often occurs that the parking brake may be frozen enough to make it difficult to release. Accordingly, a suggestion has been made that at some cold district, if without the parking brake being used at the time of parking of a vehicle, an engagement member in an automatic transmission is engaged with a to-be-engaged member with, for example, the automatic transmission set to a parking range, the movement of the vehicle is simply prevented.
Also, another suggestion has been made that if at some cold district, in order to avoid a freezing of an electric parking brake while the vehicle is parked, a sensor for detecting the ambient temperature of the vehicle detects a temperature at which the freezing takes place, the electric parking brake can be released. In this connection, see, for example, Japanese Patent Publication No. 2005-082035.
According to the technique discussed above, the electric parking brake is released and thus the movement of the vehicle is inhibited by the parking lock mechanism for the automatic transmission. However, the parking lock mechanism for the automatic transmission is an auxiliary mechanism and a burden tends to be imposed on the automatic transmission to such an extent as to trigger a problem on the state of engagement between the engagement member and the to-be-engaged member in the automatic transmission. Once this problem occurs, it may often occur that the vehicle will undesirably move.